Bump tensorflow from 2.5.3 to 2.6.4 in /examples/nlp/python_bert_squad (#1219)

Bumps [tensorflow](https://github.com/tensorflow/tensorflow) from 2.5.3 to 2.6.4.
- [Release notes](https://github.com/tensorflow/tensorflow/releases)
- [Changelog](https://github.com/tensorflow/tensorflow/blob/master/RELEASE.md)
- [Commits](https://github.com/tensorflow/tensorflow/compare/v2.5.3...v2.6.4

)

---
updated-dependencies:
- dependency-name: tensorflow
  dependency-type: direct:production
...
Signed-off-by: dependabot[bot] <support@github.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>
Co-authored-by: Chris Austen <causten@users.noreply.github.com>

examples/nlp/python_bert_squad/requirements_bertsquad.txt

-tensorflow==2.5.3
+tensorflow==2.6.4
 onnxruntime
 tokenizers
\ No newline at end of file